Method and apparatus for staggered start-up of a predefined, random, or dynamic number of flash memory devices

ABSTRACT

A method, apparatus, and manufacture for memory device startup is provided. Flash memory devices are configured such that, upon the power supply voltage reaching a pre-determined level, each flash memory is arranged to load the random access memory with instructions for the flash memory, and then execute a first portion of the instructions for the flash memory. After executing the first portion of the instructions for the flash memory, each separate subset of the flash memories waits for a separate, distinct delay period. For each flash memory, after the delay period expires for that flash memory, the flash memory executes a second portion of the instructions for the flash memory.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/716,719, filed May 19, 2015, which is a continuation of U.S. patentapplication Ser. No. 14/099,340, filed Dec. 6, 2013, now U.S. Pat. No.9,036,423, issued May 19, 2015, which is a continuation of U.S. patentapplication Ser. No. 13/162,520, filed Jun. 16, 2011, now U.S. Pat. No.8,625,353, issued Jan. 7, 2014, all of which are incorporated byreference herein in their entirety.

TECHNICAL FIELD

The invention is related to computer-readable memory, and in particular,but not exclusively, to an apparatus, method, and manufacture for astaggered start of flash memories in a memory module.

BACKGROUND

Various types of electronic memory have been developed in recent years.Some exemplary memory types are electrically erasable, programmable readonly memory (EEPROM) and electrically programmable read only memory(EPROM). EEPROM is easily erasable but lacks density in storagecapacity, where as EPROM is inexpensive and denser but is not easilyerased. “Flash” EEPROM, or flash memory, combines the advantages ofthese two memory types. This type of memory is used in many electronicproducts, from large electronics like cars, industrial control systems,and etc. to small portable electronics such as laptop computers,portable music players, cell phones, and etc.

Flash memory is generally constructed of many memory cells where asingle bit is held within each memory cell. Yet a more recent technologyknown as MirrorBit™ Flash memory doubles the density of conventionalFlash memory by storing two physically distinct bits on opposite sidesof a memory cell. The reading or writing of a bit occurs independentlyof the bit on the opposite side of the cell. A memory cell isconstructed of bit lines formed in a semiconductor substrate. An oxidenitride-oxide (ONO) dielectric layer is formed over the top of thesubstrate and bit lines. The nitride serves as the charge storage layerbetween two insulating layers. Word lines are then formed over the topof the ONO layer perpendicular to the bit lines. Applying a voltage tothe word line, acting as a control gate, along with an applied voltageto the bit line allows for the reading or writing of data from or tothat location in the memory cell array. MirrorBit™ Flash memory may beapplied to different architectures of flash memory, including NOR flashand NAND flash.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the present invention aredescribed with reference to the following drawings, in which:

FIG. 1 illustrates a block diagram of an embodiment of a system;

FIG. 2 illustrates a block diagram of an embodiment of a memory that maybe employed an embodiment of the system of FIG. 1;

FIG. 3 illustrates a block diagram of an embodiment of a NOR memoryarray;

FIG. 4 shows a cross-sectional side view of an embodiment of a coresection of the memory of FIG. 2;

FIG. 5 illustrates a flow chart of an embodiment of a process; and

FIG. 6 illustrates a block diagram of an embodiment of a system thatincludes the memory device of FIG. 2, in accordance with aspects of theinvention.

DETAILED DESCRIPTION

Various embodiments of the present invention will be described in detailwith reference to the drawings, where like reference numerals representlike parts and assemblies throughout the several views. Reference tovarious embodiments does not limit the scope of the invention, which islimited only by the scope of the claims attached hereto. Additionally,any examples set forth in this specification are not intended to belimiting and merely set forth some of the many possible embodiments forthe claimed invention.

Throughout the specification and claims, the following terms take atleast the meanings explicitly associated herein, unless the contextdictates otherwise. The meanings identified below do not necessarilylimit the terms, but merely provide illustrative examples for the terms.The meaning of “a,” “an,” and “the” includes plural reference, and themeaning of “in” includes “in” and “on.” The phrase “in one embodiment,”as used herein does not necessarily refer to the same embodiment,although it may. Similarly, the phrase “in some embodiments,” as usedherein, when used multiple times, does not necessarily refer to the sameembodiments, although it may. As used herein, the term “or” is aninclusive “or” operator, and is equivalent to the term “and/or,” unlessthe context clearly dictates otherwise. The term “based, in part, on”,“based, at least in part, on”, or “based on” is not exclusive and allowsfor being based on additional factors not described, unless the contextclearly dictates otherwise. The term “signal” means at least onecurrent, voltage, charge, temperature, data, or other signal.

Briefly stated, a method, apparatus, and manufacture for memory devicestartup is provided. Flash memory devices are configured such that, uponthe power supply voltage reaching a pre-determined level, each flashmemory is arranged to load the random access memory with instructionsfor the flash memory, and then execute a first portion of theinstructions for the flash memory. After executing the first portion ofthe instructions for the flash memory, each separate subset of the flashmemories waits for a separate, distinct delay period. For each flashmemory, after the delay period expires for that flash memory, the flashmemory executes a second portion of the instructions for the flashmemory.

FIG. 1 is a block diagram of system 190 with K*N instances of electronicdevice 100. System 190 includes processing element 112, system bus 122,power supply 139, and devices 100. Processing element 112 is incommunication with each of the devices 100 via system bus 122. Powersupply 139 is arranged to provide supply voltage VCC, which may beprovided to processing element 112 and to each of the devices 100 viasystem bus 122. Processing element 112 may include one or moreprocessing elements. In some embodiments, processing element 112 may bea microcontroller or the like.

K*N devices 100 comprise memory devices, such as flash memory devices.The flash memory devices may be organized into one or more memorymodules. In some embodiments, each memory module is a dual inline memorymodule (DIMM), or the like. In the case of flash memory devices, theamount of power used by the K*N devices 100 during start-up may causethe VCC supply voltage for one or more portions of K*N devices 100 todrop. As a result, because the VCC voltage is below the nominaloperating VCC voltage for K*N devices 100, one or more errors in readingor writing data can occur during the start up process. In order toreduce or eliminate the occurrence of such errors, some embodiments ofsystem 190 provide for a staggered start-up that occurs in stages. Thatis, rather than starting up K*N devices 100 simultaneously, system 190can manage the start-up process so that only N of K*N devices arestarted up at one time. The number of devices (N) being started upsimultaneously can be pre-defined, random, or determined dynamicallybased on the number and types of devices to be updated.

Although in general system 190 was illustrated and discussed above ashaving K sub-sets, where each sub-sets have an equal number of elementsN, the number of elements in each sub-set are not equal in allembodiments. For example, some sub-sets of de vices 100 may have moredevices 100 or less devices 100 than other sub-sets of devices 100.

Each of the devices 100 is arranged to be powered by a power supplyvoltage VCC. In some embodiments, each device 100 is a flash memorydevice that includes a random access memory (RAM) (not shown in FIG. 1).In some embodiments, each device 100 is a flash memory device where allof the flash memory devices 100 are powered by a single VCC power supply139. In some embodiments, devices 100 includes K sub-sets, which areeach configured such that upon the power supply voltage VCC reaching apre-determined level, each device 100 is arranged load the RAM withinstructions for the device 100, execute a first portion of theinstructions for the device 100, and after executing the first portionof the instructions for the device 100, employing a countdown timer towait for a particular delay period after executing the first portion ofthe instructions for the flash memory. Each of the K sub-sets has adifferent delay period. For example, a first sub-set of devices 100 maywait for a first delay period after executing the first portion of theinstructions, and a second subset of devices 100 may wait for a seconddelay period after executing the first portion of the instructions,where the second delay period is different from the first delay period.In some embodiments, other subsets of devices 100, if there are othersubsets, may each have still different delay periods. Each device 100,after waiting for the delay period for that subset, executes a secondportion of the instructions for the device 100. In this way, thestart-up of subsets of devices 100 are staggered relative to othersubsets of devices 100.

FIG. 2 shows a memory environment in which embodiments of the inventionmay be employed. Not all the components illustrated in the figures maybe required to practice the invention, and variations in the arrangementand type of the components may be made without departing from the spiritor scope of the invention. For example, although some embodiments of theinvention described in the context of a MirrorBit™ NOR flash memory, thefabrication described herein may be employed in manufacturing othertypes of microelectronic memories or devices such as other various typesof flash memory.

As shown, memory 200 includes arrayed memory 210 and memory controller230. Memory controller 230 is arranged to communicate addressing dataand program data over signal path 206. For example, signal path 206 canprovide 8, 16, or more I/O lines of data. Signal path 206 may be anembodiment of a portion of system bus 122 of FIG. 1 in some embodiments.Memory controller 230 is also configured to access arrayed memory 210over signal path 203. For example, memory controller 230 can read,write, erase, and perform other operations at portions of arrayed memory210 via signal path 203. In addition, although shown as single lines,signal path 203 and/or signal path 206 may be distributed across aplurality of signal lines and/or bus lines.

Arrayed memory 210 includes memory sectors 220 (identified individuallyas sectors 1-i) that can be accessed via memory controller 230. Memorysectors 220 can include, for example, 256, 512, 1024, 2048 or moresectors having memory cells that can be individually or collectivelyaccessed. In other examples, the number and/or arrangement of memorysectors can be different. In one embodiment, for example, sectors 220can be referred to more generally as memory blocks and/or can beconfigured to have a configuration that is different than a bit line,word line, and/or sector topology. Memory sectors 220 may also include atrim sector that is not accessible by normal addressing, as discussed ingreater detail below.

Memory controller 230 includes decoder component 232, voltage generatorcomponent 234, and controller component 236. In some embodiments, memorycontroller 230 may be located on the same chip as arrayed memory 210. Inother examples, other implementations of memory controller 230 arepossible. For example, memory controller 230 can include a programmablemicrocontroller.

Decoder component 232 is arranged to receive memory addresses viaaddressing signal path 206 and to select individual sectors, arrays, orcells according to the architecture of arrayed memory 210.

Decoder component 232 includes, for example, multiplexer circuits,amplifier circuits, combinational logic, or the like for selectingsectors, arrays, and/or cells based on any of a variety of addressingschemes. For example, a portion of a memory address (or a grouping ofbits) can identify a sector within arrayed memory 210 and anotherportion (or another grouping of bits) can identify a core cell arraywithin a particular sector.

Voltage generator component 234 is arranged to receive one or moresupply voltages (not shown in FIG. 2) and to provide a variety ofreference voltages required for reading, writing, erasing,pre-programming, soft programming, and/or under-erase verifyingoperations. For example, voltage generator component 234 can include oneor more cascode circuits, amplifier circuits, regulator circuits, and/orswitch circuits that can be controlled by controller component 236.

Controller component 236 is arranged to coordinate memory accesses suchas reading, writing, and erasing; and other operations of memory 200. Inone embodiment, controller component 236 is arranged to receive andtransmit data from an upstream system controller (e.g., processingelement 112 of FIG. 1). Such a system controller can include, forexample, a processor and a static random access memory (SRAM) that canbe loaded with executable processor instructions for communicating oversignal path 106. In another embodiment, controller component 236 as wellas other portions of memory controller 230 may be embedded or otherwiseincorporated into a system controller or a portion of a systemcontroller. Controller component 236 may include, for example, aprocessor and a random access memory (RAM) 237 such as static randomaccess memory (SRAM) that can be loaded with executable processorinstructions for communicating over signal path 206. Controllercomponent 236 may include a read-only memory (ROM) 238. The processor incontroller components 236 enables actions by executingprocessor-executable coded encoded in RAM 237. RAM 237 may loadprocessor-executable instructions from another processor-readable mediumsuch as ROM 238, a hard drive, arrayed memory 210, and/or the like.

Embodiments of controller component 236 can include a state machineand/or comparator circuits. State machine and comparator circuits caninclude any of a variety of circuits for invoking any of a myriad ofalgorithms for performing reading, writing, erasing, or other operationsof memory 200. State machines and comparator circuits can also include,for example, comparators, amplifier circuits, sense amplifiers,combinational logic, or the like.

In some embodiments, memory 200 is a flash-based memory includingflash-based memory cells, such as flash-based NOR cells, NAND cells, orhybrids of the two. In some embodiments, memory 200 is a MirrorBit™flash memory.

FIG. 3 illustrates a block diagram of an embodiment of memory device300, which may be employed as an embodiment of memory device 100 ofFIG. 1. Memory device 300 includes memory array 302 and individualmemory cells 303 located within memory array 302. Memory cells 303 arearranged in N+1 rows and M+1 columns in memory array 302. In oneembodiment, each row of memory array 302 is accessed by two of the bitlines BL0 to BLN. Each column of memory array 302 is accessed by one ofword lines WL0 to WLM. Accordingly, each of memory cells 303 can beaccessed by activating the corresponding bit lines and a correspondingword line of the cell. In one embodiment, each column of memory array302 defines a data word. If N+1 has a value of 8, for example, the cellsin each column of memory array 302 define a byte of data.

Memory cells 303 may be flash memory cells which store bits in differentways in different embodiments. In various embodiments, a single cell maystore one or more bits. For example, some memory cells are single celldevices, some memory cells are dual cells devices, and in someembodiments, more than one distinct level of threshold voltage may beused to represent more than one bit per cells, as discussed in greaterdetail below. In some embodiments, flash memory stores information in anarray of memory cells made from floating-gate transistors. In, forexample, a NOR gate flash, the transistors resemble a standardmetal-oxide-semiconductor field-effect transistor (“MOSFET”) except thatthe transistor has two gates, a floating gate and a control gate,instead of one. On top is the control gate (“CG”), as in othermetal-oxide-semiconductor transistors, but below this there is afloating gate (“FG”) insulated all around by an oxide layer. The FG isinterposed between the CG and the MOSFET channel. Because the FG iselectrically isolated by an insulating layer, any electrons placed on itare trapped there and, under normal conditions, will not discharge formany years. When the FG holds a charge, it screens (partially cancels)the electric field from the CG, which modifies the threshold voltage(“V_(T)”) of the cell. The threshold voltage of a MOSFET is usuallydefined as the gate voltage where an inversion layer forms at theinterface between the insulating layer (oxide) and the substrate (body)of the transistor. During read-out, a voltage is applied to the CG, andthe MOSFET channel will become conducting or remain insulating,depending on the V_(T) of the cell, which is in turn controlled by thecharge on the FG. The current flow through the MOSFET channel is sensedwhich permits a determination of the voltage threshold for the device,which in turn provides information about the binary data stored withinthe device.

In a single cell device, each control gate of a transistor stores asingle charge amount that represents the stored information. In itsdefault or “un-programmed” state, it is logically equivalent to a binary“1” value, because current will flow through the channel underapplication of an appropriate voltage to the control gate.

In a dual cell device, each control gate stores two charge amounts thatrepresent the stored information. That is, two physically distinctquantities of charge are stored on opposite sides of the floating gate.Reading or writing data on one side of the floating gate occursindependently of the data that is stored on the opposite side of thefloating gate. In this technology, the FG is split into two mirrored orcomplementary parts, each of which is formulated for storing independentinformation. Each dual cell, like a traditional cell, has a gate with asource and a drain. However, in the dual cell the connections to thesource and drain may be reversed in operation to permit the storage ofthe two bits. Each of the memory cells is comprised of multi-layers. Acharge-trapping dielectric layer is formed over a semiconductorsubstrate. The charge-trapping dielectric layer can generally becomposed of three separate layers: a first insulating layer, acharge-trapping layer, and a second insulating layer. Word-lines areformed over the charge-trapping dielectric layer substantiallyperpendicular to the bit lines. Programming circuitry controls two bitsper cell by applying a signal to the word-line which acts as a controlgate, and changing bit line connections such that one bit is stored bythe source and drain being connected in one arrangement and thecomplementary bit is stored by the source and drain being connected inanother arrangement.

In a single-level cell (“SLC”) device, each cell stores only one bit ofinformation, either the cell is “un-programmed” (has a “1” value) or“programmed” (has a “0” value). There also exist multi-level cell(“MLC”) devices that can store more than one bit per cell by choosingbetween multiple levels of electrical charge to apply to the floatinggates of its cells. In these devices, the amount of current flow issensed (rather than simply its presence or absence), to determine moreprecisely the level of charge on the FG.

As one example, a dual cell device may also be a MLC device that storesfour-bits-per-cell so that one transistor equates to 16 differentstates. This enables greater capacity, smaller die sizes and lower costsfor the flash devices.

Memory device 300 further includes controller 336, decoder 381, anddecoder 382.

Decoder 381 and decoder 382 can each receive address bus informationfrom controller 336 and can utilize such information to facilitateaccessing or selecting the desired memory cell(s) (e.g., memorylocation(s)) associated with the command, and to provide the neededvoltages to the bit lines (decoder 381) and the word lines (decoder 382)according to timing that is controlled by controller 336.

Decoder 381 may also include a sector decoder in some embodiments. Assuch, decoder 309 may be arranged to facilitate accessing or selectionparticular column or grouping of columns within memory device 300. Forexample, a grouping of columns may define a sector, and another groupingof columns may define another sector. In another embodiment, portion 301may include an array decoder for to a particular memory array 304. Inaddition, embodiments of array decoders can be configured to workseparately or in conjunction with a sector decoder.

Memory controller 336 is also configured to control the activation andde-activation of individual word lines WL0 to WLM for reading, writing,and/or erasing to memory array 302. For example, memory controller 310can provide a select signal to decoder 382 to select one of the columnsWL1 to WLM to activate that column. Further, memory controller 336 canprovide a select signal to decoder 381 for selecting particular rows BL0to BLN (or sector) to be written to or read from.

FIG. 4 shows a cross-sectional side view of a memory cell in coresection 401.

Memory cell 440 includes a portion of substrate 405, dielectric spacerlayer 443, channel region 444, source/drain regions 442 a and 442 b, andlayered stack 445, including charge trapping component 446 and a portionof core polysilicon line 441.

In operation, core polysilicon line 441 and source/drain regions 442 aand 442 b are configured to provide electrical potential(s) to memorycell 440 for trapping charge at charge trapping component 446. A bit is“programmed” when it is trapping a charge and “unprogrammed” when it isnot trapping charge. To trap charge, charge trapping component 446employs tunneling layer 447, charge trapping layer 448, and dielectriclayer 449. In general, tunneling layer 447 provides a tunneling barrier,charge trapping layer 448 is a layer that is configured to store charge,and dielectric layer 449 electrically isolates charge trapping layer 448from core polysilicon line 441. In one embodiment, memory cell 440 is aone bit memory cell that is configured to store up to two logic states.In another embodiment, memory cell 440 can store more than two logic (orbit) states.

In some embodiments, charge trapping component 446 is anoxide-nitride-oxide (ONO) layer in which dielectric layer 449 is anoxide (such as silicon dioxide), charge trapping layer 448 is a nitride,and tunneling layer 447 is an oxide (such as silicon dioxide). In oneembodiment in which charge trapping layer 448 is a nitride, chargetrapping layer 448 may be a silicon-rich nitride (SiRN) or astoichiometric silicon nitride. Dielectric spacer layer 443 may be anitride spacer, an oxide-nitride spacer, other type of spacer composedof one or more dielectric materials, or the like.

Modern semiconductor devices are typically created as integratedcircuits manufactured on the surface of a substrate of semiconductormaterial, which is typically a wafer formed by slicing a single crystalingot growth by a Czochralski process. Various devices are formed on thewafer using a series of steps that include deposition, removal processes(such as etching), patterning, and doping. Few steps or many hundreds ofsuch steps may be used in various designs. The patterning steps may beperformed by photolithography or other lithographic methods. Forexample, the wafer may be coated with a photoresist, which is exposedwith a device that transmits light through a photomask, exposingportions of the wafer not blocked by the photomask to light. The exposedregions are removed so that the photoresist remains only in areas thatwere not exposed to light. This allows a layer to be etched according tothe pattern on the photomask. After the devices have been formed on thewafer, various back-end processing and packaging is performed, includingproperly interconnecting the devices and bringing metal lines to thechip edge for attachment to wires.

A designer creates the device design in accordance with a set of designrules provided by the fabricator, and creates a series of design filesbased on the design, which may be stored in a machine-readable medium.Various design tools may be used by the designer in creating the design,simulating the design, and checking the design for layout rulesviolations. When completed, the design files are provided to thefabricator, which are used to generate photomasks for use in thefabricating the device. The design ales may be communicated in differentways, including over a network.

FIG. 5 illustrates a flow chart of an embodiment of a process (580).Process 500 happens to each flash memory device in a group of flashmemory devices when VCC reaches a pre-determined value, at which pointthe process begins at a start block.

The process then moves to block 582, wherein in each flash memory (e.g.100 of FIG. 1 or 200 of FIG. 2), a RAM (e.g., RAM 237 of FIG. 2) of theflash memory is loaded with instructions. The process then advances toblock 584, where each flash memory executes a first portion ofinstructions. The process then proceeds to block 586, where each subsetof flash memory devices waits for a particular delay, where the delay ofeach subset is distinct from the delay of each other subset of flashmemory devices. Waiting for the delay is accomplished by employing acountdown timer.

The process then moves to block 588, where each flash memory, uponcompletion of waiting the delay, executes a second portion of theinstructions. Because each subset has a different delay, the start-upsof the various subsets of flash memories are staggered relative to eachother. The process then advances to a start block, where otherprocessing is resumed.

In one particular, specific embodiment, the staggered start isaccomplished as follows. The following embodiment in no way limits theinvention; rather, the purpose is to describe a particular embodiment indetail without in any way limiting the invention to the details of theparticular embodiments described.

In one embodiment, a server device, which may be an embodiment of system190 of FIG. 1, includes a controller chip (which may be an embodiment ofprocessing element 112 of FIG. 1) and 16 DIMMs all powering off of thesame motherboard. Each DIMM includes 144 flash memory devices (which maybe embodiments of devices 100 of FIG. 1 and/or memory device 200 of FIG.2). The controller chip and each of flash memory devices receive VCCfrom the motherboard. When the server device is powered on, power supplyvoltage VCC ramps upward. When VCC reaches the power on reset (POR) trippoint, roughly 1.55 Volts in some embodiments, each of the flash memorydevices receives a jump start command, causing it to load instructionsfrom its ROM (e.g., 238 of FIG. 2) onto the SRAM (e.g., 237 of FIG. 2)of the flash memory device and begins executing the instructions loadedfrom ROM. As these instructions are executed by each device, theinstructions cause the device to enter into a test mode in which data isread from the trim sector of the flash memory and written directly toSRAM. The trim sector is a portion of the arrayed memory (e.g., 210)that is not accessible by normal addressing, and is used for operationof the flash memory, which includes the initial conditions that theflash memory was tested under, including the erase verify point and theprogram verify point. It may also include redundancy data, such as a mapof which sectors are good and which sectors are bad.

While in test mode, each flash memory executes code loaded from the trimsector. The code instructs the flash memory to look up a value whichrepresents a number of wait states for the flash memory to wait beforeresuming execution. In some embodiments, each DIMM has nine columns, 0through 8, and the value is the column number of the flash memorylooking up the value, from 0 to 8. Each wait state may be a certaininterval of time, such as 128 microseconds. Accordingly, for example,the flash memories in the first column, column 0, have no delay, theflash memories on column 1 have 128 microseconds of delay, the flashmemories column 2 have 256 microseconds of delay, and so forth. Eachflash memory employs a countdown counter for the delay in which theflash memory delays for the appropriate number of clock cycles. When thecountdown timer expires, execution of the code in the SRAM resumes. Theflash memory does not fully come up until the execution of the code thatoccurs until the SRAM resumes, after the delay. After the delay, theflash memory executes all the way up and is powered cleanly.

In some embodiments, staggering the start of the flash memory devices inthis manner (where all of the flash memory devices are powered from asingle power supply voltage) may reduce overall noise levels and keeppeak current demand down during power-up conditions.

Although a particular embodiment is discussed above, many variations arewithin the scope and spirit of the invention. For example, in someembodiments, rather than having a fixed delay based on column number,each subset of flash memory devices may use a random delay.

Embodiments of the memory device can be incorporated into any of avariety of components and/or systems, including for example, a processorand other components or systems of such components. FIG. 6 shows oneembodiment of system 690, which may incorporate memory 620, which is anembodiment of memory device 100 of FIG. 1. In some embodiments,processor 692 is an embodiment of processing element 112 of FIG. 1.Memory 620 can be directly or indirectly connected to any one ofprocessor 692, input devices 693, and/or output devices 694. In oneembodiment, memory 620 may be configured such that it is removable fromsystem 690. In another embodiment, memory 620 may be permanentlyconnected to the components or a portion of the components of system690.

In many embodiments, memory 620, processor 692, input devices 693,and/or output devices 694 of system 690 are configured in combination tofunction as part of a larger system. For example, system 690 may beincorporated into a cell phone, a handheld device, a laptop computer, apersonal computer, and/or a server device. In addition or alternatively,system 690 can perform any of a variety of processing, controller,and/or data storage functions, such as those associated with sensing,imaging, computing, or other functions. Accordingly, system 690 can beincorporated into any of a wide variety of devices that may employ suchfunctions (e.g., a digital camera, an MP3 player, a UPS unit, and soon).

The above specification, examples and data provide a description of themanufacture and use of the composition of the invention. Since manyembodiments of the invention can be made without departing from thespirit and scope of the invention, the invention also resides in theclaims hereinafter appended.

The invention claimed is:
 1. An apparatus, comprising: a power supply;at least one memory module coupled to the power supply comprising aplurality of subsets of memory devices, wherein each of the plurality ofsubsets of memory devices comprises a plurality of memory devices; andone or more processors configured to access one or more of the pluralityof subsets of memory devices based on a voltage of the power supplyreaching a predetermined level; wherein the at least one memory moduleis configured to be removable from the apparatus.
 2. The apparatus ofclaim 1, wherein the at least one memory module is a dual inline memorymodule (DIMM).
 3. The apparatus of claim 1, wherein the one or moreprocessors are configured to provide a processing function of a cellphone.
 4. The apparatus of claim 1, wherein the one or more processorsare configured to provide a processing function of a laptop computer. 5.The apparatus of claim 1, wherein each memory device of the plurality ofmemory devices comprises a flash memory device.